1. Field of the Invention
The present invention relates to an optical disc and a material for a substrate thereof. More specifically, the present invention relates to an optical disc with fewer loads to the environment such as CD, DVD, blue-ray disc and advanced optical storage (AOD), and a material for a substrate thereof.
2. Description of the Prior Art
One example of this kind of conventional optical disc is disclosed in Japanese Patent Laying-open No. 2000-11448 [G11B 7/24].
In the degradable optical recording medium in Japanese Patent Laying-open No. 2000-11448, the substrate and the protective layer are formed of biodegradable resin, and the reflective film uses aluminum.
An optical disc with a substrate using biodegradable resin is proposed in the prior art of Japanese Patent Laying-open No. 2000-11448. However, such an optical disc has been not yet become commercially practicable. This is because the substrate of an optical disc is required to have high levels of transparency, transferability and mass-producibility but biodegradable resin does not meet all these requirements.
More specifically, biodegradable resin, polylactic acid-based resin in particular, is of high flowability and adhesiveness to an injection molding die, and thus it is necessary to add a mold release agent for removing the resin from the die. Adding a too large amount of mold release agent would decrease the transparency of the resin, and in reverse, the addition of a too small amount of mold release agent would make it hard to remove the substrate from the die. Thus, it is difficult to achieve high levels of transferability and mass-producibility.
Besides, in order the substrate of polylactic acid-based resin to satisfy the requirements for the substrate of an optical disc, high levels of transparency and transferability, it is necessary to use a kind of polylactic acid-based that is suitable for the substrate of an optical disc.